This invention relates generally to the determination of various parameters in a subsurface formation penetrated by a wellbore. More particularly, this invention relates to the determination of formation parameters through the use of an evaluation tool featuring one or more devices that can protect the tool and/or the wellbore during evaluation.
Typical drilling techniques use a special fluid (drilling mud) that provides many important benefits to the drilling process, such as cooling the drilling bit, carrying the drilled cuttings to the surface, reducing the pipe friction and the risk of pipe sticking, and in some instances powering a downhole drilling motor (mud motor). Another important function of the drilling mud is to hydraulically isolate the well bore by allowing some of its content to slowly build an isolating layer (mud cake) over the well bore internal surface, thus protecting the sub surface formations from being invaded by the aforementioned drilling fluids.
It is known in the art of formation pressure measurement that the quality of such formation pressure measurements is dependant on the presence of a tight, impermeable mudcake. It is also known in the art of formation pressure measurement that the integrity of such mudcake is reduced by the dynamic erosion generated by the drilling mud being circulated in the annular space between the drilling pipe and the borehole. A consequence of this latter effect, usually called supercharging, leads to pressure measurements that are not representative of the surrounding formation. It is also known in the art of well drilling that maintaining drilling mud circulation at all times during the drilling process is desirable for its positive effects on reducing pipe sticking and the ability to control the behavior and the stability of the borehole.
Oil well operation and production, known in the art, involves monitoring of various subsurface formation parameters. One aspect of formation evaluation is concerned with the parameters of reservoir pressure and the permeability of the reservoir rock formation. Periodic monitoring of parameters such as reservoir pressure and permeability indicate the formation pressure change over a period of time, which is needed to predict the production capacity and lifetime of a subsurface formation. Present day operations typically obtain these parameters through wireline logging via a xe2x80x9cformation testerxe2x80x9d tool. This type of measurement requires a supplemental xe2x80x9ctripxe2x80x9d, in other words, removing the drill string from the wellbore, running a formation tester into the wellbore to acquire the formation data and, after retrieving the formation tester, running the drill string back into the wellbore for further drilling.
The availability of reservoir formation data on a xe2x80x9creal timexe2x80x9d basis during well drilling activities can be a valuable asset. Real time formation pressure obtained while drilling will allow a drilling engineer or driller to make decisions concerning changes in drilling mud weight and composition as well as borehole penetration parameters at a much earlier time to thus promote the safety aspects of drilling. The availability of real time reservoir formation data is also desirable to enable precision control of drill bit weight in relation to formation pressure changes and changes in permeability so that the drilling operation can be carried out at its maximum efficiency.
It is also possible to obtain reservoir formation data while the drill string with its drill collars, drill bit and other drilling components are present within the well bore, thus eliminating or minimizing the need for tripping the well drilling equipment for the sole purpose of running formation testers into the wellbore for identification of these formation parameters.
Various devices have been developed to evaluate formations, such as the devices disclosed in U.S. Pat. Nos. 5,242,020, issued to Cobern; 5,803,186, issued to Berger et al.; 6,026,915, issued to Smith et al.; 6,047,239, issued to Berger et al.; 6,157,893, issued to Berger et al.; 6,179,066, issued to Nasr et al.; and 6,230,557, issued to Ciglenec et al. These patents disclose various downhole tools and methods for collecting data from a subsurface formation. At least some of these devices relate to downhole testing tools with probes having sealing and/or extension mechanisms that enable the probe to contact the borehole.
While tools have been developed to improve contact with the borehole during sampling and/or testing, there remains a need to protect the probe and/or borehole surrounding the testing area to prevent erosion during data collection. It is, therefore, desirable to have a wellbore instrument, such as a formation fluid pressure testing and/or sampling device, which protects the wellbore as tests are performed and/or samples taken.
An aspect of the invention relates to a downhole tool for collecting data from a subsurface formation. The tool comprises a housing, a probe and a protector. The housing is positionable in a wellbore penetrating the subsurface formation. The probe is carried by the housing and extendable therefrom. The probe is positionable adjacent to the sidewall of the wellbore and is adapted to engage the formation. The protector is positioned about the probe and adapted for movement between a retracted position adjacent to the housing and an extended position engaging the sidewall of the wellbore. The protector has an outer surface adapted to engage the sidewall of the wellbore whereby the wellbore surrounding the probe is protected.
Another aspect of the invention relates to a downhole tool for collecting data from a subsurface formation. The tool includes a housing adapted for axial connection in a drill string positioned in a wellbore penetrating the subsurface formation. The tool also includes a first actuator system carried at least partially by the housing. The tool also includes a probe carried by the housing that is adapted for movement by the first actuator system between a retracted position within the housing and an extended position sealingly engaging the wellbore wall. The tool also includes a protector positioned about the probe, the protector operatively coupled to a second actuator, wherein the protector is adapted for movement by the second actuator system between a retracted position adjacent to the housing and an extended position engaging the wellbore wall such that the protector engages the wellbore wall.
Another aspect of the invention relates to a method for measuring a property of fluid present in a subsurface formation. A downhole tool is positioned in a wellbore penetrating the subsurface formation, the downhole tool having a probe extendable therefrom. The probe is moved into sealed engagement with the wellbore wall. A protector is positioned into sealed engagement with the wellbore wall surrounding the probe. Data is collected from the formation.
Other aspects of the invention will become apparent from the following discussion.